The present invention discloses a method of testing a partially assembled multi-die device (1) by providing a carrier (300) comprising a device-level test data input (12) and a device-level test data output (18); placing a first die on the carrier, the first die having a test access port (100c) comprising a primary test data input (142), a secondary test data input (144) and a test data output (152), the test access port being controlled by a test access port controller (110); communicatively coupling the secondary test data input (144) of the first die to the device-level test data input (12), and the test data output (152) of the first die to the device-level test data output (18); providing the first die with configuration information to bring the first die in a state in which the first die accepts test instructions from its secondary test data input (144); testing the first die, said testing including providing the secondary test data input (144) of the first die with test instructions through the device-level test data input (12); and collecting a test result for the first die on the device-level test data output (18). Consequently, a die of a partially assembled multi-die device such as a System-in-Package may be tested using its integrated boundary scan test architecture.